Malware is any software that functions to benefit a third party rather than the user.
If your installer/updater is installing some app/toolbar/etc in addition to the application I want it to install -- that's malware.
If your installer/app/updater is changing settings in my browser or any other application on my system -- that's malware.
I want to write a letter, if your "letter writing app" is sending a copy of the letter or meta-data about the letter or my writing of the later to a third party -- that's malware.
If I'm playing your off-line single-player game and you're collecting data on how I play it -- that's malware.
If I'm playing your on-line multi-player game and you're doing anything with the data I'm sending you other than sending it to the other players -- that's malware.
If your search engine is doing anything with the search request I'm sending you other than fulfilling my search request -- that's malware.
If your app is displaying ads -- that's malware (unless it's an ad locator application).